BRPI0911162B1 - installation of bottom-to-surface connection of a rigid tube with a positively buoyant flexible tube and method of placement thereof - Google Patents

Abstract

bottom-to-surface rigid pipe assembly with a positively buoyant flexible pipe and method of laying the present invention relates to a bottom-to-surface pipe installation with at least two subsea pipes (10a, 10b) resting on the seabed, comprising: 1) a first hybrid tower comprising: a) a vertical interconnecting duct (1a) anchored (3a) to a first base and connected to said underwater seabed (10a) and whose upper end is connected to a first subsurface float (2a) and b), ensuring a first connecting tube (4a), preferably a flexible tube, the connection between a floating support (11) and the upper end of the 2) at least one second rigid pipe (1b) rising from the bottom of the sea in which it is resting (10b) or from a second subsea tube resting on the bottom of the sea to which the end is inferred. which is not anchored at the level of said first base, is connected to the subsurface where its upper end is connected to a second float (2b) situated at approximately the same depth as said first float (2a) and fixed to said first float by at least and respectively a second flexible connection tube (2b), ensuring its connection with said same floating support (11).

Description

Descriptive Report of the Invention Patent for INSTALLATION OF BOTTOM-SURFACE CONNECTION OF A RIGID TUBE WITH A FLEXIBLE TUBE OF POSITIVE FLOATABILITY AND METHOD OF PLACING THE SAME.

The present invention relates to a bottom-to-surface connection installation between an underwater tube resting on the seabed and a floating surface support, comprising a hybrid tower consisting of a flexible tube connected to a rigid riser or interconnection duct ( vertical riser), whose lower end comprises a transition piece of inertia that allows its fitting in an anchoring device comprising a base resting on the seabed.

The technical sector of the invention is, more particularly, the domain of the manufacture and installation of upright columns ("interconnection duct") of production for the underwater extraction of oil, gas or other soluble or meltable material or a suspension of matter mineral from a wellhead immersed to a floating support, for the development of production fields installed on the high seas off the coast. The main and immediate application of the invention is in the field of oil production.

The floating support generally comprises anchoring means to remain in position despite the effects of currents, winds and waves. It also comprises, in general, means of storage and treatment of oil, as well as means of unloading for transporting tankers, the latter presenting themselves at regular intervals to effect the withdrawal of production. The current name for these floating supports is the Anglo-Saxon term “Floating Production Storage Offloading” (meaning “floating storage, production and unloading medium) which uses the abbreviated term“ FPSO ”in the set of the following description.

Bottom-to-surface connections of an underwater tube resting on the seabed are known, tower-hybrid type connections comprising:

- a vertical riser whose lower end is anchored to the seabed by means of a flexible joint and connected to a said tube resting on the seabed and the upper end is stretched by a floatPetition 870190039326, from 26/04/2019, p. 5/18 pain immersed in the subsurface to which it is attached, and

- a connecting tube, in general, a flexible connecting tube, between the upper end of said riser and a floating surface support, adapting said flexible connecting tube, if necessary, by its own weight, to the shape of a curve in a plunging catenary, that is, which descends widely below the float to then rise up to the said floating support.

Also known are bottom-to-surface connections made by continuously raising to the subsurface, sturdy and rigid tubes made up of tubular steel elements of strong thickness welded or screwed together, in a catenary configuration with a continuously variable curvature over its entire length in suspension, generally called “Steel Catenary interconnection duct” (SCR) which means “steel interconnection duct in the form of catenary” and also generally called “rigid tube of the catenary type” or “duct type SCR interconnection system '.

Such a catenary tube can rise up to the surface floating support or just to a subsurface float that applies a tension to its upper end, which upper end is then connected to a floating support by a flexible dip connection tube.

The reinforced configuration catenary interconnection ducts are described in applicant's document WO 03/102350.

In WO 00/49267, it was proposed, as a connection tube between the interconnection duct, the upper part of which is subjected to the application of tension by a float immersed in the surface and the floating support, rigid tubes of the SCR type and installed the float at the head of the interconnection duct at a greater distance from the surface, namely at least 300 m from the surface, preferably at least 500 m.

In applicant's document WO 00/49267, a multiple hybrid tower was described, comprising an anchoring system with a vertical tendon consisting of either a cable or a metal bar, or a tube stretched by its upper end by a float. The lower end of the tendon is attached to a base resting on the bottom. Said tendon comprises guidance means distributed over its entire length through which a plurality of said vertical interconnection duct passes. Said base can simply be placed on the seabed and remain in place by its own weight or remain anchored by means of batteries or any other device adapted to keep it in place. In WO 00/49267, the lower end of the vertical interconnection duct is able to be connected to the end of a curved, movable sleeve, between an elevated and a low position, in relation to said base, on which this suspended sleeve is associated with a means of traction that leads it to the elevated position in the absence of the interconnection duct. This mobility of the curved sleeve allows to absorb variations in the length of the interconnection duct under the effects of temperature and pressure. At the head of the vertical interconnection duct, a stop device, attached to it, rests on the support guide installed on the float head and thus keeps the entire interconnection duct in suspension.

The connection with the underwater tube resting on the seabed is, in general, made by a portion of tube in the form of a pig's tail or in the form of an S, the said S being then carried out in either a vertical or horizontal plane, being the connection with said submarine tube, in general, carried out through an automatic connector.

The installation of this embodiment comprising a multiplicity of interconnection duct maintained by a central structure comprising guidance means is relatively expensive and complex. On the other hand, the installation must be prefabricated on land before being towed at sea and then, after arriving at the site, turned to be installed. In addition, its maintenance also requires relatively high operating costs.

In addition, because crude oil is routed over very long distances, several kilometers, it must be provided with an expensive level of extreme insulation to, on the one hand, minimize the increase in viscosity that would lead to a reduction in hourly production of wells and, on the other hand, avoid blocking the flow by paraffin deposit or hydrate formation when the temperature drops to values close to 30-40 ° C. These latter phenomena are even more critical, particularly in West Africa, where the seabed temperature is approximately 4 ° C and crude oils are paraffinic.

It is, therefore, desirable that the bottom-to-surface connections have short lengths and, therefore, that the space occupied by the different connections connected to the same floating support is limited.

It is for this reason that it is desired to provide installations capable of exploiting, from the same floating support, a plurality of bottom-to-surface connections of a hybrid type with a reduced volume and simpler to install and which can be manufactured at sea from an installation vessel. pipe.

In WO 02/066786 and WO 2003/095788, installations of hybrid towers that require the application of flexible joints between the vertical interconnection duct and the base were described because the angular variations, generated by the movements of the FPSO and the action of the undulation and the chain over the tubes and the float that apply a tension to the vertical portion of the tube, are important, reaching 5 to 10 ° and these variations prevent the use of a rigid connection fitted to said base. These flexible joints are very delicate and costly to manufacture because they consist of stacks of layers of elastomer and steel reinforcements and must withstand fatigue throughout the life of installations that exceed 20-25 years or even more. In addition, the presence of the float creates a discontinuity of tension at the level of a gooseneck, at the interface between the substantially vertical rigid tube and the flexible tube in catenary configuration, which impairs the overall stability at the level of that interface and affects the mechanical strength of the installation.

In WO 02/103153, an attempt was made to provide an installation that could be manufactured entirely on land, namely with regard to the assembly of rigid tubes resting on the seabed and the vertical interconnection ducts that ensure the bottom-to-surface connection. On the other hand, in WO 02/103153, an attempt was made to implement an installation whose placement on the seabed did not require any flexible articulated joint at the bottom of the tower. For this purpose, the underwater tube resting on the seabed is connected to said vertical interconnection duct by a flexible tube element maintained by a base resting on the seabed. The connection of the lower end of the vertical interconnection duct and the end of the tube resting on the seabed, by means of the said flexible tube element and maintained by said base, is pre-assembled on land before being towed into the sea and deposited on the seabed where the base is then anchored. However, this embodiment has some disadvantages because this anchoring system requires considerable buoyancy elements for the towing and curling phase to balance the weight above the waterline of said base structure and the flexible connection elements they are subjected to major fatigue throughout the life of the facilities that reach and exceed 25-30 years.

In addition, in all installations described in the aforementioned prior art, the vertical interconnection duct is stretched by a subsurface float and the connection between the vertical interconnection duct and the floating support is made by a flexible tube in a plunging catenary configuration. , whose end is connected to the upper end of said vertical interconnection duct by a gooseneck device. This way of connecting the upper end of the vertical interconnection duct with the floating support presents certain drawbacks in terms of mechanical resistance, in terms of the discontinuity of tension created by the gooseneck connection piece and due to the application of tension to the interconnection duct. vertical by a very bulky float, the latter being subjected to the action of currents and undulation, which generates, for this type of connection, very important angular variations of the upper part of the interconnection duct, the latter reflecting at the base of the interconnection product, at the level of the flexible articulation so strongly requested.

GB-2024766 describes a vertical interconnection duct connected to a flexible tube in a dipping catenary configuration, with the end of the flexible tube connected to the said interconnection duct having a curvature imposed by a vertical cross-section with a rested circular shape. in the upper part of a toric-shaped float, the said trough, functioning as a swan neck and avoiding radii of curvature that are too small, which can lead to the crushing of said flexible tube. This embodiment does not allow the wear of the flexible pipe to be avoided in terms of its interaction with the said rail, which affects the intrinsic ability of the connection between the vertical interconnection duct and the flexible pipe in terms of mechanical resistance over time.

An objective of the present invention is, therefore, to provide an installation of bottom-to-surface connections with hybrid towers, of reduced volume, of simple placement and can be manufactured at sea from a pipe installation vessel, but whose anchoring system has a great resistance and a reduced cost and whose methods of manufacture and placement of the different constituent elements are simplified and, also, of reduced cost, being able to be carried out at sea, also, from an installation vessel.

Another objective is to provide an installation that does not require the application of flexible joints, namely at the base of the vertical interconnection duct.

Another objective of the present invention is to provide a bottom-to-surface connection installation, as described above, which requires the application of a single connection element, namely, a single automatic connector, between the lower end of the vertical interconnection duct and the end of the tube resting on the seabed.

For this purpose, the present invention provides a bottom-to-surface connection installation, namely at great depth, exceeding 1000 m, comprising:

a - at least one rigid riser, substantially vertical, called a vertical interconnection duct, fixed at its lower end to an anchoring device on the seabed, and b - at least one flexible connection tube that ensures the connection between a floating support and the upper end of said vertical interconnection duct, c - one end of said flexible tube is preferably directly connected by a flange system, at the upper end of said vertical interconnection duct, and d - the end The bottom of said vertical interconnection duct comprises an end tube element which forms a transition piece of inertia whose variation in inertia is such that the inertia of said end tube element, at its upper end, is substantially identical to that of the tube element of the main section of the vertical interconnection duct to which it is connected, increasing said inertia of element d and terminal tube, progressively, to the lower end of said inertial transition piece, comprising a first fixing flange which allows the lower end of said vertical interconnection duct to be fitted at the level of said anchoring device on the seabed, characterized per:

- a terminal part of the flexible tube, on the side of its junction with the upper end of said interconnection duct, has positive buoyancy and at least the upper part of said vertical interconnection duct also has positive buoyancy, so whereas the positive buoyancy of said end part of the flexible tube and said upper part of the vertical interconnection duct allows the application of tension to said interconnection duct in a substantially vertical position and the alignment or continuity of curvature between the end of said end part the flexible tube and the upper part of said vertical interconnection duct at the level of its connection, said positive buoyancy being introduced by a plurality of coaxial peripheral floats, regularly spaced and / or by a continuous coating of positive buoyancy material, and

- said flexible tube end part having positive buoyancy extends for a part of the total length of the flexible tube, whereby the flexible tube has an S-shape, with a first flexible tube portion on the side of said floating support a curvature concave in the form of a catenary with a plunging catenary configuration and with the said remaining end part of said flexible tube having a convex curvature in the form of inverted catenary due to its positive buoyancy, the end of said end part of flexible tube being at the end level top of said interconnection duct, preferably located above and substantially in alignment of the 7- \ L \ axis of said interconnection duct, at its upper end.

Here, the term “vertical interconnection duct” is used to account for the theoretical position of the interconnection duct when it is at rest, and it should be understood that the axis of the interconnection duct can present angular movements in relation to the vertical and move according to a cone with angle α whose apex corresponds to the point of attachment of the lower end of the interconnection duct on said base. The upper end of said vertical interconnection duct can be slightly curved. Therefore, it is understood that the "end of the flexible tube substantially in alignment with the axis Z-iZ) of said upper interconnecting duct" that the end of the inverted catenary curve of said flexible tube is substantially tangent to the end of said duct vertical interconnection. In any case, in the continuity of curvature variation, that is, without a singular point, in the mathematical sense.

Here, "inertia" means the moment of inertia of said inertial transition tube element in relation to an axis perpendicular to the axis of said inertial transition tube element, which reflects the flexural stiffness in each of the planes perpendicular to the axis XX 'of symmetry of said tube element, this moment of inertia being proportional to the product of the section of matter by the square of its distance from said axis of the tube element.

It is understood by “continuity of curvature” between the upper end of the vertical interconnection duct and the flexible part presenting a positive buoyancy, that said curvature variation does not present a singular point, such as a sudden variation in the angle of inclination of its tangent or an inflection point.

Preferably, the slope of the curve formed by the flexible tube is such that the slope of its tangent in relation to the axis Ζ _Ί Ζ \ of the upper part of said vertical interconnection duct increases continuously and progressively from the point of connection between the upper end of the vertical interconnection duct and the end of said positive floating buoyancy end part, with no inflection point and no curvature reversal point.

The installation according to the present invention therefore prevents the application of tension to the vertical interconnection duct by a float on the surface or subsurface, in which its upper end would be suspended, on the one hand and, on the other hand, avoid connecting said plunging flexible tube through a gooseneck device, as existing in the prior art. This results not only in greater intrinsic reliability in terms of mechanical resistance in the time of connection between the vertical interconnection duct and the flexible tube, because the devices of the swan neck type are fragile, but, above all, this type of installation confers an increased stability in terms of the angular variation (y) of the excursion angle of the upper end of the vertical interconnection duct in relation to a theoretical vertical rest position, because this angular variation is reduced, in practice, to a maximum angle that does not exceed 5 ^o , in practice, approximately 1 to 4 ^o with the installation according to the invention, while in the prior art embodiments, the angular excursion could reach 5 to 10 ° or even more.

Another advantage of the present invention derives from the fact that, due to this reduced angular variation of the upper end of the vertical interconnection duct, it is possible to perform, at the level of its lower end, a rigid fitting on a base resting on the seabed, without resorting to a transition piece of inertia that is too considerable and therefore too expensive. It is, therefore, possible to avoid the application of a flexible joint, in particular of the flexible ball joint type, as the junction between the lower end of the interconnection duct and said fitting comprises a transition piece of inertia.

The positive buoyancy of the interconnecting duct and the flexible tube can be introduced in a known manner by coaxial peripheral floats surrounding said tubes or, preferably, treating the rigid tube of the vertical interconnection duct, by a coating of positive buoyancy material. preferably and equally constituting an insulating material, such as syntactic foam, in the form of a wrapper surrounding said tube. These buoyancy elements that are resistant to very strong pressures, that is, pressures of about 10 MPa per 1000 m of water, are known to the person skilled in the art and are available from the BALMORAL (UK) firm.

More particularly, the positive buoyancy will be distributed, evenly and evenly, over the entire length of said end portion 10a of the flexible tube and over at least said upper part 9b of said rigid tube.

Preferably, in order to give maximum flexibility to the bottom-to-surface connection assembly, said end part of the flexible tube having positive buoyancy extends over a length of 30 to 60% of the total length of the flexible tube, from one preferably, about half the total length of said flexible tube.

More particularly, said flexible tube has positive buoyancy over a length corresponding to 30 to 60% of its total length, preferably about half of its total length.

The part of flexible dipping tube, that is, of negative buoyancy, may be all the shorter as the anchoring of the floating support11 on the surface will be rigid.

More particularly, in order to give the bottom-surface connection assembly adequate flexibility, said positive buoyancy exerted on the terminal part of the flexible tube and at least the upper part of the interconnection duct, must exert a vertical tension on the foundation at the lower end of said rigid tube as a function of the water depth according to the following formulation: F = kH, where F is said vertical tension expressed in tons, H is the referred depth expressed in meters and k is a factor between 0.15 and 0.05 preferably equal to about 0.1.

If the overall positive buoyancy is distributed evenly and evenly over the entire length of the rigid tube and over a said end part of the flexible tube, said positive buoyancy must allow to obtain a resulting vertical impulse of 50 to 150 kg / m, that is, said necessary buoyancy should correspond to the apparent weight of said rigid pipe and said flexible pipe end part added with an additional buoyancy of 50 to 150 kg / m.

In a preferred embodiment of a bottom-to-surface connection installation, it comprises the following characteristics, according to which:

- said vertical interconnection duct is connected, at its lower end, to at least one tube resting on the seabed, and

- said anchoring device comprises a support and connection device fixed to a base placed and anchored on the seabed, and

- said tube resting on the seabed comprises a first rigid end tube element integral with said base resting on the seabed and said first end tube element is held firmly in relation to said base, with, at its end, a first part of connecting element, preferably a male or female element of an automatic connector, and

- said first fixing flange at the lower end of said inertial transition piece is fixed to a second fixing flange at the end of a second curved rigid element, integral with said support and connection device fixed on said base and supporting, fixedly and rigidly, said second curved rigid tube element, the other end of which comprises a second part of connecting element complementary to said first part of connecting element and connected to it when said support and connection is fixed to said base.

It is understood that the static geometry of said first rigid tube element at the termination of said tube resting on the seabed, in relation to said base and the static geometry of said second curved rigid element, in relation to said support device and fixed connection to said base, allow to position the respective ends of said, first and second, rigid tube elements, in order to facilitate the connection of complementary parts of automatic connectors after the support and connection device is fixed in said base.

Also, preferably, the bottom surface connection installation has the characteristics according to which:

- said base is anchored to the seabed by a first tubular pillar that passes through a hole that crosses said base, said first pillar being inserted into the ground at the bottom of the sea and cooperating its upper part with the base so to allow the anchoring of said base, and

- said support and connection device supporting said second curved rigid tube element comprises a second tubular pillar, called tubular anchoring insert, inserted into said first tubular anchoring pillar of said base, said base comprising a locking device which retains said tubular anchoring insert within said first tubular pillar in the case of pulling up said second tubular pillar.

Preferably, said first and second pillars are joints of conventional unitary rigid tube elements or portions of unitary element of rigid tubes, said second pillar being shorter than said first pillar.

This system of anchoring the base and fixing said support and connection device to the lower end of said transition piece of inertia on said base is particularly advantageous for the following reasons.

First, the combination of the first pillar and tubular anchoring insert constitutes a guiding system, which makes it possible to match said first connecting element parts and second connecting element part with the ends, on the one hand, of the end tube of the tube resting on the seabed which is positioned firmly in relation to said base and, on the other hand, of the end of said rigid tube element positioned firmly in relation to said support device.

The transverse stresses or shear stresses that result from the bending moment that occurs at the level of the seabed, at the level of the lower end of the vertical interconnection duct at the level of that base, resulting from the angular variations of the interconnection duct in the its upper end, are not transmitted to said base, but to said first anchoring pillar, which extends deep into the seabed for a length of 30 to 70 m. Thus, it is possible to make said base of relatively low volume and weight, which allows it to be able to descend relatively easily from the surface, integrally with said first tube end element of the tube resting on the seabed.

More particularly, said tubular anchoring insert is positioned on the axis of said inertial transition piece and said second rigid tube element supported by said support and connector device is arched or curved so that said first part of connecting element of the automatic connector type is separated laterally from the rest of said support and connection device and said second part of connecting element of the automatic connector type, at the end of said first end rigid tube element of said tube resting on seabed, solidary with said base, is also separated from the hole of said base and from said support and connection device whose said anchoring insert is inserted inside said first anchoring pillar.

In this embodiment, said first end tube element of said tube resting on the seabed can preferably be equally curved, to correctly match the end of said second curved rigid element and allow easy connection by an underwater ROV automaton on the seabed.

More particularly, said inertia transition tube element has a cylinder-conical shape, in which:

- the thinner upper end of the transition piece has an internal diameter and thickness substantially equal to the internal diameter and thickness of the lower end of said vertical interconnection duct, to which it is attached, and

- the lower end of the transition piece, on the side of said first fixing flange, has an internal diameter substantially equal to that of the lower end of said vertical interconnection duct, but a greater thickness, preferably equal to 3 to 10 times that of the lower end of said vertical interconnection duct.

These inertia transition tube elements can measure from 15 to 50 m in length. More particularly, the cylindrical part extending from 3 to 5 m in length and the conical part extending from 10 to 47 m in length. The manufacture of these parts is very expensive because they must be carried out with the help of very thick tubes, but of variable thickness, joined together and then machined in a lathe of very large dimensions to obtain the conical shape. The production of these parts is very expensive because, in order to obtain a good result, it is necessary that the tube assembled by welding before finishing the machine is perfectly straight and, in addition, the lathes capable of precision machining of parts from 20 to 30 m in length. length are difficult to find and have a very high operating cost.

In certain extreme cases, cylindrical transition parts cannot be made of steel and require the use of titanium, which further increases the cost and complexity.

According to another original feature of the present invention, said inertial transition end tube element comprises a main rigid tube element and at least one, preferably a plurality n of coaxial reinforcement tube elements arranged coaxially with respect to said main tube element, each said reinforcement tube element having an internal diameter greater than the outer diameter of the main tube element and, if applicable, the other (s) element (s) of reinforcement tube that contains (containing), the different main tube elements and the reinforcement tube element (s) positioned with one of its ends located on the same level according to the direction of the ZiZ \ axis of symmetry of those tube elements and each reinforcement tube element having a length (hj, with i = 2 an) less than the hi of the main tube element and, if applicable, that of the other elements s of reinforcement tube (hj_i) it contains, the annular spaces (Di-d _{i +} i) being between the different tube elements filled with a solid filling material and the different elements (8b-8d) being the main tube and tube coaxial reinforcement bars fixed to the same bottom plate consisting of said first fixing flange.

Advantageously, according to the invention, said annular space is completely filled with the same solid filler material, preferably comprising an elastomer material, still preferably, based on polyurethane, having a hardness shore greater than or equal to A50, still preferably from A50 to D70 and said inertial transition element is covered by a corrosion resistant elastomeric covering material, preferably of polyurethane type, having the said inertial transition end tube element a substantially cylinder-conical shape due to its coating by said cover material.

According to the present invention, because the annular space is completely filled with the same filling material and the covering material gives the transition piece a cylinder-conical shape, a continuous diameter variation is obtained, in cross section , of the part and with the same filler material along the entire height of the transition part, which results in a progressive and continuous variation of inertia, that is, without discontinuity of inertia. In addition, the application of an elastomeric covering material introduces corrosion protection that guarantees greater longevity to the said transition piece, which is subjected to considerable mechanical stress and would present, without this protection, a reduced longevity.

It is understood that said solid filler material must have a compressive strength in order to transfer the shear forces to the reinforcement tube element of higher order «i + 1» proportionally to the deformation of said coaxial element that contains, of order "i", under the effect of a flexed effort. In practice, the solid filler material should have a Poisson's ratio of 0.3 to 0.49, preferably 0.4 to 0.45.

This filling material can be an elastomer, such as rubber or polyurethane, alone or in combination with sand.

It is understood that this type of inertial transition tube element is advantageous due to its simplicity of manufacture and, therefore, much less expensive than the tube elements presenting a cylinder-conical transition piece with wall of varying thickness of the prior art. .

According to other specific characteristics of said inertial transition end tube element of the present invention:

- for practical manufacturing and cost reasons and also to increase the flexibility and, therefore, the longevity of the transition piece, said covering material and said filling material comprise the same elastomer material, preferably at the same time. ba17 se of polyurethane.

- said solid filler material comprises a shore hardness polyurethane A90 or A95.

- the solid filler material comprises an elastomer loaded with particulate material, preferably sand.

In a variant of the embodiment, the solid filler material is in the form of a hydraulic binder, such as cement, optionally loaded with particulate material, preferably sand.

In another embodiment, said solid filler material is in the form of particulate material, preferably sand and / or a hydraulic binder, such as cement:

- the difference between the inside diameter of said main pipe element and the outside diameter of said larger diameter reinforcement pipe element is equal to 3 to 10 times the thickness of said main pipe element and the number of said reinforcement elements coaxial values is n = 2 to 4,

- the difference in length between the different coaxial reinforcement tube elements (hj, -hj + i) is substantially constant and equal to (hj x n)

- the annular space between two of said tube elements is greater than or equal to the thickness of said tube element of lesser thickness and less than or equal to twice the thickness of said tube element of greater thickness delimiting said annular space,

- the length of said main pipe element is 10 to 50 m, preferably 20 to 30 m and comprises 2 or 3 of said coaxial reinforcement elements,

- said main tube element and coaxial reinforcement tube elements are each constituted by all or part of a unitary element of conventional tube, namely submarine tube conventional in steel, or each, constituted by several unitary elements of conventional tube mounted end to end and preferably maintained coaxially by centering wedges distributed evenly along their longitudinal direction and over the circular section in their annular spaces.

An important advantage of the bottom surface connection installation of the present invention also resides in the simplicity of its placement on the seabed.

The present invention therefore also provides a method of placing a bottom-surface connection installation according to the invention on the seabed, comprising the following successive steps in which:

1. the anchor device is lowered to the bottom of the sea, and

2. a rigid tube is descended constituting a vertical interconnection duct, directly fixed, at its upper end, to an end of said flexible tube having a positive buoyancy end portion, the other end of said flexible tube being suspended by a float subsurface, and

3. the lower end of said transition piece is fixed by fitting at the level of said anchoring device, and

4. the end of said flexible tube suspended in said float is displaced and fixed or connected to said floating support.

Preferably, a method of placing a bottom-to-surface connection installation according to the invention, comprises the following successive steps, in which:

1. a solidary base is descended to the bottom of the sea with said first rigid tube element, said base comprising a through hole and

2. a first tubular anchoring pillar is lowered to the bottom of the sea, which is inserted into the bottom of the sea through said hole in the base, to anchor said base to the seabed, and

3. the rigid tube is descended to the bottom of the sea from a surface vessel, constituting said vertical interconnection duct, directly fixed, at its upper end, to said flexible tube, said transition piece being, at the lower end of said interconnection duct, attached to said support and connection device, supporting said second curved rigid tube element, as well as said anchoring insert, and

4. said support and connection device is fixed to said base by inserting said anchoring insert within said first tubular pillar, and

5. preferably, said anchoring insert within said first tubular pillar is blocked by a locking device, and

6. the connection of said first curved rigid element and second curved rigid element is carried out, and

7. the descent of said flexible tube ends with a terminal portion of positive buoyancy, with the other end of said flexible tube suspended in a subsurface float, and

8. moves and then fixes or connects the other end of said flexible tube to said floating support.

This method, according to the invention, is particularly simple and, therefore, advantageous in terms of placement. This simplicity results from the fact that the anchoring function on said base is satisfied by the said anchoring insert, on the underside of said support and connection device and by the bending moments suffered by the inertial transition piece being absorbed by the first pillar. of anchoring tucked into the seabed and not by said base, so that it is possible to use a base with a relatively low weight and volume.

Other features and advantages of the present invention will appear better in the light of the following detailed description, made in an illustrative and non-limiting way and using drawings, in which:

figure 1 is a side view of a bottom-surface connection installation 1 according to the invention comprising a rigid interconnection duct-type tube 9, fitted, in the lower part, in a first pillar 6 that crosses a base 4 and is connected, at its upper end 9b, to a flexible tube 10 floating on a terminal part 10a of its length, the other end of the tube being connected to an FPSO 12 (“Floating Production Storage Offloading”),

- figure 2A is a side view of the bottom surface connection installation 1 at its base during laying from a work vessel 20,

- figure 2B is a side view of placing said first anchoring pillar 6 on a base that supports the end of an underwater tube resting on the seabed,

figure 2C is a side view of the lower end of the interconnection duct 9 with an inertial transition piece 8 at the level of its connection with a support and connection device 5 comprising a tubular anchoring insert 5 within said pillar 6 anchoring,

- figure 3 is a side view of the installation of the deep surface connection, during placement, after engaging the anchoring insert 5e on the anchoring pillar 6,

- figures 3A and 3B represent, in side and sectional view, two basic variants of the connection to a pipe resting on the seabed of a bottom-to-surface connection installation according to the invention,

- figure 4 is a cross-sectional and side view of a massive steel transition piece 8, conical in shape, installed at the lower end of the interconnection duct 9,

- figures 5A-5B-5C are seen in cross-section and in side view of a preferred version of making a transition piece consisting of stacks of coaxial steel tubes, the interstices being filled with plastic materials in figures 5B and 5C,

figure 6 is a diagram illustrating the variation of the inertia of the transition pieces according to figure 5C.

In figure 1, a bottom surface connection installation 1 is shown, which connects an underwater tube 2 resting on the seabed 3 to a floating support 12 of the FPSO type on a surface tied by anchor lines 12a.

An installation according to the invention comprises, from support 12 on the surface to a base 4 on the seabed, the following elements:

a) a flexible tube 10 comprising a first concave part 10b extending from the end 10e of the flexible tube attached to the floating support 12 to about half of the flexible tube, in the form of a dip catenary configuration due to its negative buoyancy, up to a point of inflection in 10d roughly half the length of the flexible tube, the terminal part 10a extending from the central point 10d of inflection to the end 10c of the flexible tube showing positive buoyancy due to a plurality of floats 10f, of preferably, evenly spaced along and around said flexible pipe end portion 10a, and

b) a rigid steel ascending tube 9 or "vertical interconnection duct" equipped with buoyancy means, not shown, such as syntactic foam semi-casings, preferably evenly distributed over all or part of the length of said rigid tube and comprising, at its lower end, an inertial transition piece 8 equipped with a first fixing flange 9a at its lower end. The first fixing flange 9a is attached to a second fixing flange 5a that constitutes the upper part of a support and connection device 5, the same anchored to a first pillar 6 with the base 4 resting on the seabed, allowing the said support and connection device 5 the connection of the lower end of the interconnection duct 9 to a tube 2 resting on the seabed, as explained below.

The flexible tube has a continuous curvature variation, first concave, in part 10b with a plunging catenary configuration and then convex in the terminal portion 10a of positive buoyancy with a 10d point of inflection between the two, thus forming a It is arranged on a substantially vertical plane.

The geometric curve formed by a uniform weight suspension tube subject to gravity, called “catenary”, is a mathematical function of the hyperbolic cosine type (Coshx = (e ^x + e ^x ) / 2, connecting the abscissa and the ordinate of a any point on the curve according to the following formulas:

y = R ₀ (cosh (x / R ₀ ) - 1) R = Ro. (Y / Ro + 1) ² in which:

- x represents the distance in the horizontal direction between the point of horizontal tangency and a point M of the curve,

- y represents the altitude of the point M (x and y are, therefore, the abscissae and ordinates of a point M of the curve in relation to an orthonormal system whose origin is at that point of tangency)

- R _o represents the radius of curvature at said point of horizontal tangency.

- R represents the radius of curvature at point M (x, y).

Thus, the curvature varies along the catenary from the surface (for a plunging catenary) or from its terminal part at the upper end of the interconnection duct (for an inverted catenary) where its radius has a maximum value R _max , up to the horizontal tangency point (which is the low point of the plunge catenary 10b and the high point of the inverted catenary 10a), where its radius has a minimum value R _m , _n (or R _o in the above formula).

In operation, as shown in figure 1, when the upper part of the rigid tube 9 is inclined with an inclination y with respect to the vertical ZZ ', the end 10c of the terminal portion 10a of the positive buoyancy of the flexible tube remains substantially in axial alignment Z ^ Z 'of the upper end 9b of the rigid tube 9, and in any case, in continuity of curvature variation with the upper end 9b of the rigid tube, which can also be slightly curved. Here it is understood by «continuous variation of curvature» that there is no singular point in the mathematical sense in this variation of curvature. This gives a better mechanical resistance to the watertight fixation 11 between the two tubes and allows to avoid the application of a gooseneck device, as used in the prior art.

The interest of this flexible tube is to allow, due to its initial plunging portion 10b, to cushion the excursions of the floating supports 12 in order to stabilize the end 10c of the flexible tube connected to a rigid tube rising from the vertical interconnection duct 1.

The end of the portion of the floating end portion 10c of the flexible tube has a first fixing flange element 11 with the upper end of a rigid tube extending from the seabed at the level of a base 4 resting on the seabed.

The vertical interconnection duct 9 is "stretched", on the one hand, by the buoyancy of the terminal part 10a of the flexible tube, but on the other hand and above all, by floats regularly distributed, at least on the upper part 9b, preferably , along the entire rigid tube, namely in the form of syntactic foam, which serves, advantageously and at the same time, as an insulation and buoyancy system. These floats and this syntactic foam can be distributed along and around the rigid tube over its entire length or, preferably, only over a portion of its upper part.

Thus, if the base 4 is at a depth of 2500 meters, the cover of the rigid tube of syntactic foam may be limited to a length of 1000 m from its upper end, which allows the use of a syntactic foam that must resist at a pressure lower than that which would exist if it had to withstand pressures that go up to 2500 m and, therefore, having a radically reduced cost in relation to a syntactic foam and must withstand the referred depth of 2500 m.

The rigid tube 1 according to the invention is therefore "stretched" without the application of a float on the surface or subsurface, as in the prior art, which limits the effects of the current and the ripple and, consequently, radically reduces the excursion the high part of the vertical interconnection duct and, therefore, the stresses at the base of the interconnection duct at the level of the socket.

To give the bottom-surface connection a great deal of flexibility, an advantageous vertical tension is applied to the foundation depending on the height of the water according to the following formulation: F = kH, where F is expressed in tonnes , H expressed in meters, k between 0.15> k> 0.05, preferably k »0.1.

If the positive buoyancy is spread over the entire length of the rigid tube, it thus represents 50 to 150 kg of resulting thrust per meter of tube.

It is preferably distributed continuously along the rigid tube, as well as along the end portion 10a of the flexible tube. On the latter, the distribution is generally made by buoys 10f spaced from each other and distributed regularly over the portion 10a, each representing the equivalent of a few meters of the necessary impulse, for example, for a spacing of 5 to 10 m, the resulting thrust being required for each float from 250 to 1500 kg per float.

It must be understood that the overall buoyancy corresponds to what is generally called “Archimedes impulse” or “Apparent Weight” on each part of the bottom-surface connection: corresponding, on the one hand, to the buoyancy required to counteract the respective apparent weight of the rigid tube and the flexible tube and, on the other hand, to the additional buoyancy necessary to apply tension that allows to obtain, thus, a resulting vertical impulse of 50 to 150 kg / m as previously described.

Proceeding thus, and the global buoyancy at the level of the transition between rigid tube and flexible tube substantially constant, results in a continuity of curvature variation between the upper end of said rigid tube and the end of said flexible tube that is connected to it, without a point singular, in the mathematical sense of the term.

The flexible pipe interconnection duct 10 and the connection of the flanges 9a, 5a between the lower end in the inertial transition piece 8 and the connection support device 5, give rise to watertight connections between the pipes in question.

The base 4 resting on the seabed supports a first curved or arcuate end tube element 2a of said tube resting on the seabed 2. This first curved or arched end tube element 2a comprises, at its end, a first male or female part of an automatic connector 7b, which is separated, laterally, in relation to a through hole 4a of said base, but positioned fixed and determined in relation to the ZZ 'axis of said orifice.

The support and connection device 5 supports a second curved rigid tube element 5b comprising, at its upper end, said second fixing flange 5a and, at its lower end, a second female or male part of an automatic connector 7a, complementary to part 7b.

A first anchoring tubular pillar 6 is lowered from a surface-mounted vessel 20 and then, preferably, threaded through knownly applied strokes, through a hole 4a that runs vertically from one side to the other. the other, the base 4 until a peripheral growth 6a at the upper end of said first pillar 6 cooperates with a complementary shape 4c at the top of said hole 4a of the base. The orifice 4a is slightly larger than the first pillar 6 to let it slide freely. And when the striking of the first pillar is completed, the base 4 is thus nailed to the ground without being able to move laterally or rotate around any horizontal axis.

Eventually, a plurality of holes and referred to first pillars 6 is foreseen.

In the method of placing a bottom-surface connection installation according to the invention, the first step is to lower said base equipped with said first end element 2a of the tube resting on the surface to the bottom of the sea. seabed. After anchoring said base by said first pillar 6, the transition piece 8 is anchored at the lower end of the vertical interconnection duct by fixing on the support and connection device 5, itself anchored in said base, forming, thus, a rigid fit of the lower end of the vertical interconnection duct.

The support and connection device 5 consists of elements 5c of rigid and reinforcing structure that support said second fixing flange 5a and said second curved rigid tube element 5b, ensuring said rigid structure elements 5c, also , the connection between said second fixing flange 5a and a lower plate 5d supporting, on the bottom face, a second tubular pillar 5e called a tubular anchoring insert.

When the base 4 is anchored on the bottom 3 of the sea, as shown in figure 2A, on board the surface ship 20, the various bottom-surface connection elements are manufactured, namely the joining of sections made up of a plurality of elements conventional tubes, which are progressively lowered. First, said device 5 is connected watertightly to the lower end of the vertical interconnection duct 9 through the conical transition piece 8 and then the integrality of the vertical interconnection duct equipped with its buoyancy and, finally, the flexible connection tube equipped with its elements of fixed buoyancy in the direct continuity of the upper end of the vertical interconnection duct 9.

The assembly and installation of the rigid tube 9 is done in a classic manner, from the ship 20, by joining elements of unitary tubes or sections of unitary elements stored in the surface ship 20 and descended progressively according to a technique known to the verse in the art and described, inter alia, in earlier patent applications in the applicant's name, from a ship installing in J.

When the integrality of rigid tube 9 has been manufactured and descended to the bottom of the sea, it is known, for example, through flanges 11, the upper end of tube 9 to the end of a flexible tube 10, which, as it is unfolded from the installation vessel 20 it is presented, in the first place, in the vertical form, as shown in figure 2A, due to the fact that it floats, at least, in its terminal part 10a, by the regularly distributed buoyancy elements 10f over the terminal portion 10a.

It should also be noted that the rigid steel tube 9 can, in a known way, be a pipe-in-pipe type comprising an insulation system in the annular space between the two coaxial tubes constituting the interconnection duct 9 and , in addition, an insulation system, such as syntactic foam that serves as a buoyancy system, as described above.

When the lower end of the anchoring tubular insert 5e preferably having a slightly conical shape 5f is positioned in the vicinity and overlooking the hole 4a of the base 4, the said tubular insertion 5e is advantageously directed anchoring, more precisely, due to an automatic submarine or «ROV» 20a piloted from the surface. Said tubular insert 5e with a length of 10 to 15 m then re-enters, naturally and due to its own weight, in said first tubular anchoring pillar tucked into the seabed over a depth of 30 to 70 m.

The outer diameter of the tubular anchoring insert 5e may be slightly smaller than the inner diameter of the first pillar 6, for example, less than 5 cm, which facilitates the orientation of the tubular insert 5 within said first pillar 6, while preventing, at the same time , the transverse movements in a horizontal plane after the tubular insertion 5 is completely inserted, as shown in figure 3.

At this moment, a bolt 4b, shown in a retracted position in figure 2A, is moved in engaged position, as in figures 1 and 3, in order to block the upper plate 5d of the tubular insertion 5, within the said first pillar 6, preventing, thus, any upward displacement of the bottom-to-surface connection assembly 1 which is engaged through the connection support device 5 on the first pillar 6 attached to said base 4.

After the bolt 4b has been engaged, the unwinding of the flexible tube is terminated, as shown in figure 3, and the upper end of the flexible tube is connected to a temporary subsurface buoy 21, which is connected to a dead body 21b resting on the seabed by a cable 21a.

By doing so, the integrality of the bottom-surface connection 1 is advantageously pre-installed before the placement of the FPSO 12, which greatly facilitates operations.

After the floating support 12 is positioned on the surface, the end 10e of the flexible tube 10 is recovered, which will then be connected to said floating support FPSO 12, as shown in figure 1 and the temporary buoy 21 is recovered, as well such as its dead body 21b and its anchor line 21a.

The tubular insertion 5e transmits to the said first tubular pillar 6 the bending moments due to the shearing and transverse forces suffered at the level of the fitting of the piece 8 in the device 5.

The fastening system of the upper end of the rigid tube 9 with the flexible tube 10 and the application of tension to said tubes gives greater stability to the upper end of the rigid tube 9 with an angular variation y that does not exceed, in operation, the 5 ^o .

Thus, it was possible, according to the present invention, to make a rigid fitting of the lower end of the rigid steel tube 9 to the base 4 through the connection support device 5. For this purpose, the lower end tube element of the rigid tube 9 comprises a conical transition piece 8 whose inertia, in cross section, progressively increases from a value substantially identical to the inertia of the tube element 9 of the interconnection duct to which it is connected , in the narrow elevated part of the transition piece 8, up to a value of 3 to 10 times greater than the level of its low part connected to said first fixing flange 9a. The coefficient of variation of inertia depends, essentially, on the bending moment that must support the vertical interconnection duct at the level of said transition piece, said moment being a function of the maximum excursion of the upper part of the rigid steel tube 9, therefore , the y-angle. In order to make this transition piece 8, steels with a high elastic limit are used and, in extreme stress cases, it can be carried out to manufacture transition pieces 8 in titanium.

In figure 4, a cylindrical transition piece 8 showing a variable thickness that progressively increases from the narrow upper part 81 to the thicker lower part 82 with a constant internal diameter corresponding to the internal diameter of a conventional rigid tube and, in any case, the internal diameter of said second rigid tube member 6.

In a preferred version of the invention, shown in section and in side view in figures 5A-5B-5C, the transition piece 8 consists of a steel main tube element 8a, preferably with an internal diameter identical to that of the of the main section of the tube 9 and preferably with a thickness equal to or slightly greater than that of the main section of said tube 9 and preferably with a thickness equal to that of said second curved tube element 5b. To obtain an increase in inertia, as the flange 9a approaches, a succession of elements (8b-8d) of decreasing heights (h ₂ , h ₃ , h ₄ ) is available, having each of said coaxial tube elements an inner diameter (d ₂ - d ₄ ) greater than the outer diameter DtD3 of the preceding coaxial tube element it contains and a length or height less than the length of the preceding tube element, that is, the element tube containing or covering and a thickness depending on the desired stiffness increase.

Thus, in figure 5A, a transition piece 8 comprising a first element 8a of inner tube and three elements 8b-8c-8d of coaxial reinforcement tube with diameters d ₂ -d ₃ -d ₄ and lengths h ₂ -h ₃ -h ₄ decreasing, each of said coaxial tube elements being solidary, at its lower end, with the same said first flange 9a. In order to ensure a substantially continuous variation of inertia between the high part of reduced inertia of the transition piece 8 and the low part of strong inertia located in the connection with the flange 9a, it is advantageously injected in the annular spaces between said coaxial tube elements, a material 8 and elastomer, preferably such as a polyurethane, whose hardness is adjusted to obtain the desired stiffness variation, namely, a shore hardness from A50 to D70.

It may be sufficient to inject said rigid material 8e only into the annular interstices between the coaxial tube elements, as shown in figure 5C. However, according to the invention, a mold is installed in order to obtain a cylindrical-conical piece, as shown in figure 5B, which allows the reinforcement of the transition piece and its protection in the which refers to the aggression of the external environment by an external coating that gives it, therefore, a cylinder-conical shape with a transition of regular and continuous inertia. Care must be taken not to cover the upper part of the transition piece with a thermosetting resin over a length of 20 to 50 cm in order to be able to join it, on board the installation vessel 20, by welding, to the lower end of the rigid tube 9.

It is understood that, in order to manufacture the transition piece 8 according to the invention, proceed as follows:

- the lower end of the first longest main tube element 8a is welded to the flange 9a, and

- a first coaxial reinforcement tube element 8b is inserted around said first main tube element 8a, the lower end of which is welded to the same flange 9a, and

- the second reinforcement tube 8c is inserted around the first reinforcement tube element 8b and its lower end is welded to the flange 9a, and

- a third element of lower reinforcement tube 8d is inserted around the second element of reinforcement tube 8c and its lower end is welded to flange 9a, and

- a thermoplastic or thermoset material is injected between the various tube elements and, if necessary, the outer surface is coated with a cylinder-conical mold to obtain the required stiffness and variation of inertia and protection against corrosion .

In figure 6, diagram I of the variation of inertia, in ordinates, between the flange 9 and the upper end of the transition piece 8 of figures 5B and 5C was represented. The dashed ladder 30 represents the variation of the steel section in the absence of covering and filling material at the level of each of the elements of reinforcement tubes. The curves 31-32-33 represent the variation of the inertia (ΣΕΙ) of the transition piece 8 of figures 4 and 5C according to its length, according to the type of filling material. The curve 33, of parabolic shape, is obtained with a filling material of the type A polyurethane of shore hardness A90 or A95 and constitutes a preferred version of the invention. The curve 31 is obtained with a much harder material, such as a very high performance cement, alone or in combination with a powdery load, such as sand.

The intermediate curve 32 corresponds to the steel transition piece in figure 4.

The application of the same filler and cover material according to the cylinder-conical profile of figure 5B of polyurethane type, as previously described, preferably of hardness A90 or A95, is closer to curve 32 than curves 31 and 33 and is therefore the preferred version of the invention in terms of inertia variation.

For example, an 18 m long transition piece hi is made through a 200 mm thick flange 9a on which a main tube element 8a with an external diameter di = 323.85 mm, thickness is welded 20.6 mm and length hi = 18 m, a first coaxial reinforcement 8b with an external diameter d ₂ = 457.20 mm, thickness 12.7 mm and length h ₂ = 12m, a second coaxial reinforcement 8c with a diameter external d ₃ = 609.6 mm, thickness 6 mm and length h ₃ = 6 m. Then, a mold copy is made of everything, either in a vertical position or in an oblique position with an inclination of 5 to 30% to facilitate filling and avoid voids, using a polyurethane resin 8e of shore hardness A90 or A95. The space between the first pipe 8a and the first reinforcement 8b is 53.98 mm and the space between the second reinforcement and the first reinforcement is 70.2 mm. The increase in inertia is approximately a factor k = 3 at the level of the first reinforcement 8b and a factor k = 5 at the level of the second reinforcement 8c. Upon pouring, depression cycles in the mold are advantageously performed during filling in order to eliminate undesirable air bubbles as much as possible. In fact, because the transition piece is going to be installed at a very great depth, the hydrostatic pressure can have detrimental effects on the overall mechanical functioning after the said bubbles collapsed on itself due to the said pressure which is approximately 10 MPa per fraction 1000 m of water.

In figure 3A, the invention has been described with a base 4 placed at the same time as the underwater tube resting on the bottom, said base being stabilized by a first pillar 6 that crosses it. But it remains in the spirit of the invention if one considers, as in figure 3B, a base 4 constituted by a suction anchor, presenting an orifice, preferably circular, integrated in the said suction anchor and playing the role of pillar 6 and able to receive the anchoring insert 52. Thus, the support and connection device 5 at the lower end of the bottom-surface connection is directly attached to the suction anchor whose weight reaches 25 to 50 tons for a diameter of 3 to 5 m and a height of 20-25 m. In this configuration, the submarine tube 2 is placed independently and therefore requires a joint tube 7 made to order after installation of the bottom-surface connection and the submarine tube 2. Said connecting tube 7 then requires two automatic connectors 7a-7ai, 7b _r 7b, one at each end, while the version described using figure 3A requires only a single automatic connector 7a-7b.

The invention has been described in a preferred version manufactured and simultaneously installed on site from an installation ship 20, but remains in the spirit of the invention with a prefabrication of the complete set in a shipyard on land, with the set being towed, substantially horizontally, up to the place and then and finally, turned with a view to inserting the anchoring insert 5e in the first tubular pillar 6.

Claims (15)

1. Installation of bottom-to-surface connection, namely at great depth, exceeding 1000 m, comprising: a - at least one rigid riser, substantially vertical, called vertical interconnection duct (9), fixed at its lower end to an anchoring device (4, 5, 6) on the seabed (3), and b - at at least one flexible connection tube (10) which ensures the connection between a floating support (12) and the upper end of said vertical interconnection duct (9), c - one end of said flexible tube is directly connected in a way preferred by a flange system (11), at the upper end of the said vertical interconnection duct (9), characterized by the fact that: - the lower end of said vertical interconnection duct comprises an end tube element which forms a transition piece of inertia (8) whose variation in inertia is such that the inertia of said end tube element, at its upper end, is substantially identical to that of the tube element of the main section of the vertical interconnection duct to which it is connected, increasing said inertia of the terminal tube element (8), progressively, until the lower end of said inertial transition piece, comprising a first flange fastening device (9a) which allows the lower end of said vertical interconnection duct to be fitted (5a-5e) at the level of said anchoring device (4, 5, 6) on the seabed (3), and - a terminal part (10a) of the flexible tube, on the side of its junction with the upper end of said interconnection duct, has positive buoyancy and at least the upper part (9b) of said vertical interconnection duct also has a positive buoyancy, so that the positive buoyancy of said end part (10a) of the flexible tube and of said upper part (9a) of the vertical interconnection duct allows the application of tension to said interconnection duct in a substantially vertical position and the alignment or continuity of curvature Petition 870190039326, of 26/04/2019, p. 6/18 2 between the end of said end part (10a) of the flexible tube and the top part (9b) of said vertical interconnection duct at the level of its connection, said positive buoyancy being introduced by a plurality of peripheral coaxial floats (10f), regularly spaced and / or by a continuous coating of positive buoyancy material, and - said end part (10a) of flexible tube (10) having positive buoyancy extending for part of the total length of the flexible tube, such as the flexible tube having an S-configuration, having a first portion (10b) of tube flexible on the side of said floating support (12) a concave curvature in the form of catenary with a plunging catenary configuration and the said remaining terminal part of said flexible tube (10a) has a convex curvature in the form of an inverted catenary due to its positive buoyancy, the end (10c) of said flexible tube end part (10b) being at the level of the upper end of said interconnection duct, located above and preferably substantially in alignment of the axis (Z1Z1) of said duct interconnection at its upper end (9b). 2. Bottom-to-surface connection installation, according to claim 1, characterized by: - said positive buoyancy is evenly and evenly distributed over the entire length of said flexible tube end part (10a) and over at least said rigid tube top part (9b), preferably over the entire length of said rigid tube so as to obtain a resulting vertical thrust of 50 to 150 kg / m over the entire length of said rigid tube and the length of said flexible tube end part, and - said flexible tube (10) has positive buoyancy (10a) for a corresponding length of 30 to 60% of its total length, preferably half of its total length. 3. Bottom-to-surface connection installation according to claim 1 or 2, characterized by: - said vertical interconnection duct (9) is connected, due to its Petition 870190039326, of 26/04/2019, p. 7/18 3 lower end, at least one tube resting on the seabed (2), and - said anchoring device (4, 5, 6) comprises a support device (5) and connection fixed to a base (4) placed and anchored (6) on the seabed (3), and - said tube resting on the seabed (2) comprises a first rigid end tube element (2a), integral with said base (4) resting on the seabed (3) and said first end tube element is maintained stationary with respect to said base, with, at its end, a first part of connecting element (7b), preferably a male or female element of an automatic connector, and - said first fixing flange (9a) at the lower end of said inertial transition piece (8) is attached to a second fixing flange (5a) at the end of a second curved rigid tube element (5b), integral with said support and connection device (5a5e) fixed on said base (4) and supporting, fixedly and rigidly, said second curved rigid element (5b), the other end of which comprises a second part of connection element (7a) complementary to said first connection element part (7b) and connected to it when said support and connection element (5a-5e) is attached to said base. 4. Bottom-to-surface connection installation according to claim 3, characterized by: - said base (4) is anchored to the seabed (3) by a first tubular pillar (6) that passes through a hole that crosses (4a) said base, said first pillar (6) being buried in the ground on the seabed (3) and cooperating its upper part (60) with the base in order to allow the anchoring of said base, and - said support and connection device (5a-5e) supporting said second curved rigid tube element (5b) comprises a second tubular pillar, called tubular anchoring insert (5e), inserted into said first tubular anchoring pillar of the said base, said base comprising a locking device (4a) which retains the Petition 870190039326, of 26/04/2019, p. 8/18 4 said tubular anchoring insert (5e) within said first tubular pillar (2b) in the case of pulling up said second tubular pillar (5e). Bottom-to-surface connection installation according to claim 4, characterized in that said first and second pillars are unions of conventional unitary elements of rigid tubes, or portions of unitary element of rigid tubes, said second pillar being shorter that said first pillar. Bottom-to-surface connection installation according to claim 4 or 5, characterized in that said tubular anchoring insert (5e) is positioned on the axis of said inertial transition piece (8) and said second tube element rigid (5b) supported by said support and connector device (5a-5e) is arched or curved so that said first connector part (7a) of the automatic connector type is separated laterally from the rest of said device support and connection (5) and said second connector part (7b) of the automatic connector type, at the end of said first rigid end tube element (2a) of said tube resting on the seabed (3), solidary with said base (4), is also separated from the hole (4a) of said base and from said support and connection device (5) whose said anchoring insert is inserted within said first the anchor pillar (6). Bottom-to-surface connection installation according to any one of claims 1 to 6, characterized in that said inertial transition tube element (8) has a cylinder-conical shape in which: - the thinner upper end of the transition piece has an internal diameter (d1) and a thickness substantially equal to the internal diameter and thickness of the lower end of said vertical interconnection duct, to which it is attached, and - the lower end of the transition piece, on the side of said first fixing flange (9a), has an internal diameter (d1) sensi Petition 870190039326, of 26/04/2019, p. 9/18 the same as the lower end of said vertical interconnection duct, but a greater thickness (Ü4-di), preferably 3 to 10 times that of the lower end of said vertical interconnection duct. 8. Installation of bottom-to-surface connection, according to the Vindication 6 or 7, characterized in that said inertial transition end tube element (8) comprises a main rigid tube element (8a) and at least one, preferably a plurality (n) of elements of coaxial reinforcement tubes (8b-8d) arranged coaxially in relation to said main tube element (8a), each said reinforcement tube element (8b-8d) having an internal diameter (di + 1) greater than the external diameter (D1, Di) of the main tube element and, where appropriate, the other reinforcement tube element (s) it contains, the different main tube elements (8a) and the element (s) (s) of reinforcement tube (8b-8d) positioned with one of its ends located at the same level according to the direction of the axis of symmetry (Z1Z1) of said tube elements and showing each said reinforcement tube element (8b- 8d) a length (hi-1, with i = 2 an) less than h1 of the main pipe element and, where appropriate, that of the other reinforcement tube elements (hi + 1) it contains, the annular spaces (Di — di + 1) being between the different tube elements filled with a solid filler material (8e) and the different elements of the main tube (8a) and coaxial reinforcement tube (8b-8d) being fixed to the same lower plate (9a) constituted by said first fixing flange (9a). 9. Installation of bottom-to-surface connection, according to rei25 vindication 8, characterized by: - said annular space is completely filled with the same solid filler material, preferably comprising an elastomeric material, preferably still based on polyurethane, having a shore hardness greater than or equal to A50, on one 30 preferably from A50 to D70 and - said inertial transition element is covered by a corrosion resistant elastomer covering material, in a prePetition 870190039326, of 26/04/2019, p. 10/18 6 wound, of polyurethane type, the said inertial transition end tube element having a substantially cylinder-conical shape due to its coating by said covering material. Bottom-to-surface connection installation according to claim 8 or 9, characterized in that said covering material and said filling material comprise the same elastomeric material, preferably based on polyurethane, in a way Preferred, said solid filler material comprising an A90 or A95 shore hardness polyurethane. Bottom-to-surface connection installation according to claim 8 or 10, characterized in that said filler material comprises an elastomer loaded with particulate material, preferably sand. Bottom-to-surface connection installation according to any one of claims 8 to 11, characterized in that the length of said main tube element (8a) is 10 to 50 m, preferably 20 to 30 m comprises 2 or 3 of said coaxial reinforcement elements (8b-8d). Bottom-to-surface connection installation according to any one of claims 8 to 12, characterized in that said main tube element (8a) and coaxial reinforcement tube elements (8b-8d) are each constituted entirely by the whole or part of a conventional tube unit element, namely conventional steel submarine tube, or each consisting of several unit elements of conventional tube mounted end to end and preferably maintained coaxially by centering wedges evenly distributed along longitudinal direction and over the circular section in its annular spaces. 14. Method for placing on the seafloor (3) of a bottom-to-surface connection installation as defined in any one of claims 1 to 13, characterized in that it comprises the following successive steps in which: 1. a device (5) descends to the bottom of the sea (3) Petition 870190039326, of 26/04/2019, p. 11/18 anchoring, and 2. a rigid tube (9) descends, constituting a vertical interconnection duct, directly fixed, at its upper end, to an end (10c) of said flexible tube (10) presenting a terminal portion (10a) of positive buoyancy, the other end (10e) of said flexible tube (10) being suspended by a subsurface float (21), and 3. the lower end of said transition piece (8) is fixed by fitting at the level of said anchoring device (5), and 4. the end (10e) of said flexible tube suspended in said float is displaced and fixed or connected to said floating support (12). Method according to claim 14, for placing a bottom-to-surface connection installation as defined in any of claims 3 to 14, characterized in that it comprises the following successive steps, in which: 1. a base (4), integral with said first rigid tube element (2a), goes down to the bottom of the sea (3), said base (4) comprising a through hole (4a), and 2. a first anchoring tubular pillar (6) is lowered to the bottom of the sea (3) which is buried in the bottom of the sea (3) through said hole (4a) of the base, to anchor said base to the bottom of the sea (3), and 3. the rigid tube (9) descends to the bottom of the sea (3), from said surface vessel (20), constituting said vertical interconnection duct, directly fixed, at its upper end, said flexible tube , said transition piece (8), at the lower end of said interconnection duct, attached to said support and connection device (5), supporting said second curved rigid tube element (5b), as well as a said anchoring insert (5e), and 4. said support and connection device (5) is fixed to said base by inserting said anchoring insert (5e) into said first tubular pillar (6), and Petition 870190039326, of 26/04/2019, p. 12/18 5. preferably, said anchoring insert (5e) is locked into said first tubular pillar (6) through a locking device (4b), and 6. the first rigid tube element (5b) and the second curved rigid element (2a) are connected and 7. the descent of said flexible tube ends with a terminal portion of positive buoyancy, with the other end (10e) of said flexible tube suspended in a subsurface float (21), and 8. moves and then attaches or connects the other end (10e) of said flexible tube to said floating support (12).